The invention concerns synchronous motors of the type comprising a rotor of permanently magnetized high coercivity material, and a stator comprising at least two metal plates enclosing an induction coil, each plate having projecting poles imbricated between poles of the other plate, said poles being placed between the induction coil and the rotor.
In known synchronous motors of this type, such as that described in French Pat. No. 1,522,320, the self induction of the induction coil is low. To limit the current consumption, it is thus necessary, unless external resistive and capacitative elements are employed, to provide the induction coil with a high resistance, involving the use of a small diameter (i.e. about 0.05 mm) enamelled copper wire with a sufficient number of windings. Consequently there is a relatively great length and hence weight of wire per coil. This is a disadvantage, as low-diameter enamelled copper wire is of very high cost, and the cost of the wire may amount to 50% of the overall cost price of the motor. Moreover, heating of the coil is proportional to RI.sup.2, where R is the resistance of the coil and I the current flowing through the coil. Hence, the greater the value of R, the value of I must be consequentially reduced to limit the maximum heating of the motor. This is therefore a second disadvantage resulting from the need of employing a high resistance wire for the induction coil.